Durable uv blocking transparent coating

ABSTRACT

A coating and associated method for coating is disclosed. The coating provides a hard, transparent, UV blocking coating for a substrate. A UV blocking layer is first deposited upon the substrate, and a hard coating is deposited above the UV blocking layer. A soft coating layer may be deposited between the UV blocking layer and the hard coating. The soft and hard coating layers may both have the general composition SiO x C y . the soft and hard coating layers may be deposited by a plasma vapor deposition process.

FIELD

This disclosure relates generally to a wear resistant coating, and moreparticularly, to a durable dual layer transparent coating that includesan ultra violet (UV) blocking layer.

BACKGROUND

Plastics are finding increasing use in manufactured goods. For example,certain automobiles have plastic body panels, and aircraft have plasticinterior paneling and exterior skin panels formed of plastics andplastic composites. While plastics offer several excellent propertiesincluding light weight, formability, and low cost, plastics also havesignificant disadvantages. In general, plastic surfaces are not as hardor abrasion resistant as metal surfaces. Furthermore, while someplastics may be transparent, glass, which is much heavier and moreexpensive, remains the material of choice in certain criticalapplications such as safety glass in automobiles and in passengeraircraft windshields. Substituting polymeric materials such as stretchedacrylic or polycarbonate would lead to lighter transparencies, but wouldalso pave the way for re-designing the overall shape of cockpits, forexample. A new class of transparent composites made of glass fiberreinforced polymer have been developed that have mechanicalcharacteristics, such as tensile strength, which are comparable toaluminum. However, these transparent composites are soft and are highlysusceptible to UV, chemical attack and or mechanically induceddegradation. Currently, stretched acrylic materials are used tofabricate aircraft passenger windows. Acrylic is used because of itsflexibility, light weight, and easy formability. However, acrylic is asoft material and hence can be easily scratched. Water absorption,chemical attack, and mechanically induced scratches can lead to crazingwhen stress is applied to acrylic materials, as in a passenger windowapplication.

Industry wide, polymer based transparencies are protected against wearand other chemical/nature induced degradation through siloxane coatings.At the present time, polycarbonate and other types of polymeric windowsare protected by sol-gel based polysiloxane coatings. The term sol-gelor solution-gelation refers to materials undergoing a series ofhydrolization and condensation reactions. The sol-gel coatings arehomogeneous mixtures of a solvent, an organosilane, an alkoxide and acatalyst that are processed to form a suitable coating. The sol-gelcoatings provide high transmittance and limited durability against wearand UV induced degradation. Typically, a metal alkoxide or metal salt ishydrolyzed to form a metal hydroxide. The metal hydroxide then condensesin solution to form a hybrid organic/inorganic polymer. The ratio oforganic to inorganic components in the polymer matrix is controlled tomaximize the performance for a given application. For example,increasing the organic groups would improve flexibility but maycompromise wear and environmentally induced durability. The sol-gelcoating may include materials such as cerium or titanium to improveabrasion resistance and ultraviolet induced degradation of the coatings.A typical application process would consist of component surfacecleaning, followed by the application of the coating via a flow, sprayor dip process. The surface cleaning may be achieved by solvent wipingwith, for example, isopropyl alcohol or exposing the component to oxygenplasma. The sol-gel coatings can be cured at room temperature orelevated temperatures. For example, stretched acrylics must be cured attemperatures less than 180° F.

Aircraft cockpit windows are currently made of multi-pane glass forstrength and abrasion resistance. Efforts are on going to switch topolymeric material based flight deck windows as these materials arelight and are amenable to forming desired shapes at a low cost. Whileplastics offer several excellent properties such as light weight,formability, and low cost, plastics also have significant short comings.In general, plastic surfaces are not as hard or abrasion resistant asglass or steel surfaces. Polymeric materials are susceptible to particle(e.g. sand)/water induced erosion and chemical crazing; protective hardcoatings are needed to maintain the optical quality of the windows inuse.

In addition, while a polymeric-glass laminate has weight savings over anall glass laminate, additional weight savings could be achieved byremoval of the glass facing ply if erosion and abrasion were not aproblem. The polymeric-glass laminate also suffers from thermallyinduced stresses which degrade service life due to the thermal expansiondifference between the glass and polymeric layers. Matching contourbetween glass and polymeric plies poses manufacturing problems and oftenleads to optical and service related issues in the final part.Commercially available transparent hard coatings are in general solventbased polysiloxane. These coatings are applied through a dip, spray orfloat coat process and offer limited durability

Duplex coating schemes have been developed that offer improvedperformance. For example, a dual layer scheme has been developed thatincludes a relatively soft hard coat, such as polysiloxane with a harderbut brittle top layer. Further developments to dual layer schemesinclude a multilayer scheme as well as a dual layer coating appliedusing only plasma deposition. While these newer coating developmentsoffer outstanding durability, they transmit light over all wavelengths,including UV.

There is a need for a durable, transparent, hard coating that improvescomponent lifetime by providing UV protection. The coating shouldprovide improved resilience against chemicals commonly encountered inproduct maintenance, excellent weatherability characteristics, and UVprotection. The coating should be both hard and flexible, so that ittolerates the flexing of the polymeric material due to operation andthermal stresses. The coating should be provided by a simple process andat a low cost.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems and methods that are meant to beexemplary and illustrative, not limiting in scope. In variousembodiments, one or more of the problems described above in theBackground have been reduced or eliminated, while other embodiments aredirected to other improvements.

A first embodiment of the disclosure provides for a coating including aUV blocking layer and a hard coating layer disposed above the UVblocking layer. The hard coating layer has the general formulaSiO_(x)C_(y).

A second embodiment of the disclosure provides for an article includinga substrate and a coating deposited upon the substrate. The coatingincludes a UV blocking layer disposed upon the substrate and a hardcoating layer. The hard coating layer has the general formulaSiO_(x)C_(y).

A third embodiment of the disclosure provides for a method of forming acoating on a substrate including the steps of providing a substrate,depositing UV blocking layer upon the substrate, and depositing a hardcoating layer upon the UV blocking layer. The hard coating has thegeneral formula SiO_(x)C_(y).

One advantage of the present disclosure is to provide a transparent,hard coating with excellent durability and UV protection.

Another advantage of the present disclosure is to provide a transparent,hard coating having UV protection that improves component lifetime.

Another advantage of the present disclosure is to provide a transparent,hard coating that is both hard and flexible and provides UV protection.

Another advantage of the present disclosure is to provide a transparent,hard coating that provides improved resistance against chemicalscommonly encountered in product maintenance, which further provides UVprotection.

Another advantage is to provide a transparent, hard coating providingexcellent weatherability characteristics and UV protection.

Another advantage of the present disclosure is to provide a process forapplying a transparent, hard coating that provides UV protection.

Another advantage of the present disclosure is to provide a durablecoating that provides UV blocking.

Another advantage of the present disclosure is to provide a method offorming a coating on a substrate including the steps of applyingcoatings having differing characteristics.

Another advantage of the disclosure is to provide a method of applyingtransparent hard coating having different engineering properties likehardness and elastic modulus.

Another advantage is to provide a transparent, hard coating having UVprotection at temperatures compatible with a substrate or withoutdamaging a substrate or degrading its physical properties.

Another advantage is to provide a transparent, hard coating having UVprotection that can be substantially seamlessly varied within thecoating thickness.

Further aspects of the method and apparatus are disclosed herein. Otherfeatures and advantages of the present disclosure will be apparent fromthe following more detailed description of the preferred embodiment,taken in conjunction with the accompanying drawings that illustrate, byway of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary embodiment of an applied coating according to thedisclosure.

FIG. 2 is a graph showing the amount of light transmitted through anexemplary UV blocking coating compared with the Air Mass 1.5 solarspectrum.

FIG. 3 is a graph showing the results of a test determining the relativeadhesion of the UV blocking coating and UV dual layer coating accordingto BSS 7225 Type I and III for a dry and 24 hour water soak.

FIG. 4 is a graph showing the results of a test determining the abrasionresistance of the UV coating comparing optical haze as a function ofTaber wear cycle (ASTM D-1044) for another exemplary coating accordingto the disclosure.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawing, in which a preferred embodimentof the invention is shown. This disclosure may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of the disclosure to those skilled in the art. All compositionpercents are given as weight percents, unless otherwise specified.

FIG. 1 illustrates an embodiment of an exemplary coated article 100according to the disclosure. The coated article 100 includes a coating110 and a substrate 120. The coated article 100 may be an aircraftwindow, aircraft cockpit canopy, or other coated transparent substrate.For example, the coated article 100 may be selected from a groupincluding, but not limited to an acrylic aircraft window, an airplanecockpit, an airplane navigation light lens, and a fiberglass-epoxyradome. Additionally, the coated article 100 need not be limited to theaircraft industry. For example, the coated article 100 may further beselected from a group including, but not limited to consumer electronicssuch as polycarbonate cases for consumer electronics, cell phone touchscreens, and automotive applications such as automobile parts, panelsand windows, as well as other industry applications exposed to wear anddamage.

As can be seen in FIG. 1, in an exemplary embodiment of the disclosure,a coating 110 is disclosed that includes a first layer 130, a secondlayer 140, a third layer 150, and an optional fourth layer 160. Thefirst layer 130 is formed of a UV blocking material. The first layer 130is deposited adjacent or directly upon the substrate 220. The UVblocking material is selected to absorb UV wavelength light. In oneembodiment, the UV blocking material may be a polyurethane orpolysiloxane based material. In another embodiment, the UV blockingmaterial may be a UV blocking polymer material. For example, the UVblocking polymer material may be a polyurethane or other polymercontaining benzophenone to other phenol containing compound that absorbsUV light. In another embodiment, the UV blocking material may be a metaloxide. For example, the UV blocking material may zinc oxide, titaniumoxide, cerium oxide, or any mixture of these metal oxides. In yetanother embodiment, the UV blocking material may be a polymer materialincluding metal oxide particles. In one example, the UV blockingmaterial may be a polymer containing nano-scale particles of zinc oxide.The alternating multilayer design creates more interfaces which allowsfor any advancing crack to be deflected, thereby dissipating energy andimproving toughness.

In one embodiment, the UV blocking material may be applied by a processincluding, but not limited to, spray coating, float coating, plasmadeposition and sputtering. In one embodiment, the UV blocking layerblocks more than 97% of UV radiation up to 375 nm. In anotherembodiment, the UV blocking layer blocks for than 98% of UV radiation upto 375 nm. In another embodiment, the UV blocking layer blocks for than99% of UV radiation up to 375 nm.

The second layer 140 is a first protective layer. The first protectivelayer 140 may be a soft coating material such as a polysiloxane coating.In one embodiment, the first protective layer 140 is a polysiloxanehaving a general formula Si_(x)O_(y)C_(z). In one embodiment, the firstprotective layer 140 may be applied by a process selected from a groupincluding, but not limited to a dip process and a plasma depositionprocess. The first protective layer 140 has a first hardness and firstmodulus.

The third layer 150 is a second protective layer. The second protectivelayer 150 is a hard coating material, for example a Si_(x)O_(y)C_(z). Inone embodiment, the second protective layer 150 is deposited by plasmadeposition. The second protective layer 150 has a second hardness and asecond modulus. The second hardness is selected to be greater than thefirst hardness of the first protective layer 140. In addition, thesecond modulus is greater than the first modulus of the first protectivelayer 140. As defined herein, the term soft layer is defined as having ahardness factor less than that of an adjacent outer hard layer. Thehardness factor may be selected from the group including, but notlimited to known hardness factors including scratch hardness,indentation hardness.

The optional fourth layer 160 is an outer protective layer. The outerprotective layer 160 is a transparent hydrophobic coating. In oneembodiment, the outer protective layer 160 may be a fluorinatedhydrocarbon. In another embodiment, the outer protective layer 160 is anon-polar organosilane. The outer protective layer 160 may be applied byany suitable method, for example, but not limited to spraying, wiping,painting, and dipping. In one embodiment, the outer protective layer 160may have a thickness of between about 1 nm and about 5 nm. In anotherembodiment, the outer protective layer 160 has a thickness of betweenabout 1 nm and about 3 nm. In yet another embodiment, the outerprotective coating has a thickness of less than about 1 nm.

In addition to the outer protective layer 160 providing water repellencyto the coating 110, the outer protective layer 160 may also provide anadditional layer of physical protection for the substrate 120. In oneembodiment, the outer protective layer 160 also functions as a wearindicator. The outer protective layer 160 indicates wear when thehydrophobicity of the coating is degraded or partially degraded, thatis, when the coating 110 is less hydrophobic. The decrease inhydrophobicity indicates that some or all of the coating 110 has beenabraded away, damaged, or otherwise removed, such as for example bychemical attack or physical abrasion, and that some or all of thecoating 110 needs to be reapplied.

In an alternative embodiment, the first layer 130 and the second layer140 are combined in a single layer (not shown) having protective and UVblocking properties. In one embodiment, the single layer may be apolymer containing UV blocking components. In one embodiment, the singlelayer may be a polysiloxane containing UV blocking components. Inanother embodiment, the single layer may be a polyurethane or otherpolymer containing benzophenone to other phenol containing compound thatabsorbs UV light. In another embodiment, the single layer may be a metaloxide. For example, the single layer may zinc oxide, titanium oxide,cerium oxide, or any mixture of these metal oxides. In yet anotherembodiment, the single layer may be a polymer material including metaloxide particles. In one example, the single layer may be a polymercontaining nano-scale particles of zinc oxide.

In another alternative embodiment, a plurality of alternating layers ofa soft coating material and a hard coating material are depositedbetween the UV blocking material and the hydrophobic material.

The substrate 120 may be a metal, a rigid polymer material such as anacrylic, polycarbonate or plastic, a fiber reinforced polymer matrix, anamorphous material such as glass, or other similar material. Thesubstrate 120 may be a hard, soft, flexible or rigid material. Thecoating 210 benefits any substrate 120 where the coating 210 is harderthan the substrate 220. In one embodiment, the substrate 120 may be acommon aircraft passenger window formed of acrylic or other similarpolymeric material. For example, the coating 210 may be applied tostretched acrylic substrate, such as a stretched acrylic aircraftwindow, to improve crack growth resistance. U.S. Patent Publication No.2007/0122598A1, published May 31, 2007, and U.S. patent application Ser.No. 12/137,390, filed Jun. 11, 2008, disclose duplex coating schemesthat include soft and hard coating layers, the disclosures both of whichare incorporated by reference herein in their entireties.

The soft coating material has greater adhesion and flexibilitycharacteristics relative to the hard coating material. The greateradhesion and flexibility of the soft coating material improves theadhesion of the coating 110 to the substrate 120. The soft coatingmaterial provides a bonding layer and thus is deposited prior todepositing hard coating material. The soft coating material need not bevery thick to provide the adhesion benefit to the hard coating material.In one embodiment, the soft coating material may have a thickness ofbetween about 3 μm and 7 μm. For example, the soft coating material mayhave a thickness of about 4 μm, 5 μm, or 6 μm. The thickness of the softcoating material is sufficient to ensure the adhesion of hard coatingmaterial to substrate 120.

In one embodiment, the soft coating material has a general compositionof SiO_(x)C_(y) having about 30% to about 35% Si, about 30% to about 35%C, and about 30% to about 35% O. In one embodiment, the soft materialhas a hardness of about 0.5 GPa to about 1.5 GPa. Within thisapplication, all composition percents are provided as atomic percent.

As discussed above, the hard coating material has greater hardness,wear, and weatherability characteristics relative to the soft coatingmaterial. The greater hardness, wear, and weatherability characteristicsimprove the resistance of the coating 110 against mechanical scratching,chemical attack, and environmental degradation. In one embodiment, thehard coating material may have a thickness of between about 3 μm and 7μm. For example, the hard coating material may have a thickness of about4 μm, 5 μm, or 6 μm. The thickness of the hard coating material issufficient to provide a desired durability to the coating 110. In oneembodiment, the hard coating material has a general composition ofSiO_(x)C_(y) having about 30% to about 35% Si, about 25% to about 30% C,and about 40% to about 45% O. In one embodiment, the hard coatingmaterial has a hardness of about 1.9 GPa to about 6.0 GPa. In oneembodiment, the layer thicknesses will be in the nanometer range so thatnanostructure induced (for example Hall-Pitch effect) mechanicalstrength will be in effect.

As shown in FIG. 1, the thickness of each layer of the second layer 130and third layer 140 are approximately equal. In yet another embodiment,the layers of the second layer 130 and/or the third layer 140 may varyin thickness. In still another embodiment, the coating 210 may includemore than one soft coating material and more than one hard coatingmaterial. For example, different soft coatings materials and/ordifferent hard coatings materials may be used that vary in compositionand/or hardness.

The coating 110 improves resistance of the substrate 120 to surfaceeffects. In one embodiment, the abrasion resistance of the coating 110,as measured by the percent change in haze as measured in a Taber wearTest (ASTM D-1044-90), is more than two orders of magnitude better thanthat for a polysiloxane coated polycarbonate substrate. In oneembodiment, the erosion resistance of the coating 110, as measured bypercent change in haze as measured in a Falling Sand Test (ASTM D968-05), is more than a factor of three better than that for glass. Inaddition, the optical properties, including light transmittance in thevisible region, clarity and haze, of a substrate 120 with a coating 110disposed thereupon are approximately equal to the same properties of asubstrate 120 with a single polysiloxane coating.

In an exemplary method of forming the coated substrate 100 according tothe disclosure, a plasma based deposition technique can be used todeposit transparent silicon oxycarbide nano-layers and form thealternating soft and hard, flexible multi-layers. In this scheme,process parameters, for example, the oxygen to silicon precursor ratio,would determine coating characteristics such as hardness, modulus andcoating deposition rate.

In one embodiment of the invention, the soft and hard materials areapplied in a single step using a plasma based deposition process. Bytuning the process parameter, the present scheme allows manipulation ofindividual layer characteristics such as layer thickness, hardness andmodulus. The ability to change these coating characteristics wouldenable the applicability of the same system to process products fordifferent applications such as windows for aircraft or cell phonescreens where the requirements can be vastly different. For example,aircraft window coatings need to be hard and flexible whereas in suchapplications as consumer electronics the coatings should be resistant towear and exposure to consumables such as coke. From a manufacturingpoint of view, both the coating application cost and product thru-putare increased.

In one embodiment, the soft and hard coating layers 140, 150 are formedby depositing alternating layers of soft coating material and hardcoating material having differing SiO_(x)C_(y) compositions. The coating110 is further formed by depositing the UV blocking layer 130 andhydrophobic layer 160. The coating 110 may be formed by using a plasmabased deposition process.

The coating 110, other than the hydrophobic layer 160, may be formed ina single step continuous process or may be formed by a multiple stepdiscontinuous process. A substantially seamless material transitionexits between the alternating layers of the soft coating material andthe hard coating material, which results from the use of the plasmadeposition process to deposit both layers. In one embodiment, thecoating 110, except for the hydrophobic layer 160, is formed in a singlecoating process without removing the substrate 120 from the processchamber. In yet another embodiment, the substrate 120 is not removedfrom the process chamber and input parameters such as chemical gas flowrates, are varied during the coating process. By controlling andadjusting the deposition process parameters, individual layercharacteristics including composition, layer thickness, hardness andmodulus may be controlled and individually selected for each depositedlayer. Furthermore, deposition parameters such as bias voltage,pressure, temperature and flow rate can be controlled and adjusted toinfluence the microstructure of the coating and its relative hardness orsoftness. Thus, two coatings with the same chemical composition may havedifferent coating densities having different hardness and moduluscharacteristics.

The plasma based deposition process of the current invention uses aplasma-enhanced chemical vapor deposition (PECVD) that uses the energyof plasma electrons to disassociate process gases. The plasma sourceincludes a radio frequency or microwave power source and an appropriateapplicator. For example, a plasma reactor using microwave power at 2.45GHz may be used to dissociate and ionize the process gasses. The layerscan be deposited at low substrate temperatures of between about 20° C.to about 30° C. The PECVD conditions, such as gas flow, depositionpressure, and plasma power may be adjusted to produce a hard,transparent coating in accordance with known plasma depositionprinciples.

The process further employs the principal of Electron CyclotronResonance (ECR), in which a static magnetic field is applied along thedirection of microwave propagation. Resonance occurs when the microwaveradian frequency ω is equal to the cyclotron frequency ω_(c)=qB/m_(e),where q is the electronic charge, B is the magnetic field strength, andm_(e) is the electron mass. If f=2.45 GHz, the resonance field value is875 Gauss. At resonance, the electrons gyrate in synchronism with theoscillating microwave field. The plasma electrons are thus acceleratedby the microwave field.

The process gas used in this deposition process is oxygen used incombination with an organosilicon precursor. For example, the precursorgas may be any one of octamethycyclotetrasiloxane (C₈H₂₄O₄Si₄)), alsoknow as OMCTS, hexamethyldisiloxane (si₂C₆H₁₈O),tetramethylcyclotetrasiloxane (Si4C4H16O4), andoctamethylcyclotetrasiloxane ((SiO)₄(CH₃)₈). In one embodiment, OMCTS isused as the precursor gas. The OMCTS vapor pressure at room temperatureis approximately one Torr, which greatly facilitates vapor introductioninto the process chamber. Additionally, the Hazardous MaterialsIdentification System (HMIS®) hazard rating for OMCTS is 1-2-0, whichmeans that OMCTS is about as safe as a typical house paint. In anotherembodiment, combinations of different precursor gases may be used.

To deposit the alternating layers of SiO_(x)C_(y), the OMCTS is heatedto about 70° C. to increase vapor pressure of the OMCTS. The vapor isthen metered into the process chamber by a heated mass flow controller.The vapor is introduced just above the substrate through four portsequally spaced around the chamber, while oxygen O₂ is injected throughfour ports located under the input microwave window. The ratio of OMCTSto O₂ (OMCTS/O₂) is between about 40-60 to form a soft layer and isbetween about 15-35 to form a hard layer. In one embodiment, thesubstrate is neither heated or cooled by external systems and/ormethods, and is at ambient temperature at the start of the depositionprocess. The substrate temperature may increase as a result of thecoating deposition. In another embodiment, the substrate temperature isless than about 100° C. during the deposition.

There are two methods that can be used to deposit the UV blocking layer130. If using a solvent based coating, spry, dip or float coatingtechniques are used. These coatings include metal oxide particles, suchas zinc oxide particles, or contain an organic UV blocking material suchas a compound having a phenol group. UV blocking coatings can also bedeposited using PECVD in a process similar to the hard coat deposition.For example, zinc oxide coating can be deposited using a diethylzinc andoxygen in a PECVD process.

The outer protective layer 160 may be applied by a spray or dip process.In one example, a thin layer of the coating solution is brushed on thesubstrate. The substrate is allowed to dry and any resulting haze isgently buffed out with a microfiber towel.

In one embodiment, substrate 120, prior to being loaded into a plasmadeposition chamber for the application of the coating 110, may be firstchemically cleaned to remove contaminants such as hydrocarbons and otherundesirable materials. The cleaning process may be accomplished using,for example, ultrasonic cleaning in solvents or aqueous detergents. Oncethe desired vacuum conditions are obtained, substrate 120 may be sputtercleaned using inert ions and/or oxygen ions. Once the cleaning step iscomplete, the hard coating application can commence.

FIG. 2 shows the test results for a 0.125 inch thick quartz glass samplehaving a coating prepared in accordance with the present disclosure.Quartz is transparent in the UV region and thus the effect of UVblocking characteristics of the coating can be clearly exemplified. Thespectrum of light transmitted through the UV blocking layer was obtainedwith a UV-Vis spectrometer. The transmitted light, or in other words,the light that passed through the UV blocking layer, was compared withthe spectrum of solar light on the Earth's surface, as provided by AirMass 1.5 common standard. As can be seen in FIG. 2, nearly all of the UVlight, as defined as wavelengths of less than 390 nm, was blocked by theUV blocking layer. The peak in transmittance at 270 nm is not of concernbecause there is not any irradiance in Air Mass 1.5 at that wavelength.

In another test, 0.125 inch thick transparent composite samples having acoating prepared in accordance with the present disclosure wereprepared. These samples and an uncoated sample were exposed to 300 kJ ofUV light in an Atlas Ci4000 WeatherOmeter according to SAE J 1960. TheWeatherOmeter exposes samples to UV light at a controlled temperatureand humidity to simulate typical conditions. In this text, a visualinspection of the coated samples did not reveal any change in color tothe coated samples, while the uncoated samples were yellow and had highhaze.

FIG. 3 shows test results for another set of samples prepared accordingto the present disclosure. In this test, the adhesion of the coating to0.125 inch transparent composite substrates was tested by forming across hatch scribe of 5 parallel lines set 45 deg off upon the samplesand applying a tape over the scribed area. Additional samples wereprepared in accordance with the present disclosure. Two sets of sampleswere prepared for each coating. One set was scribed and immediatelytested. The second set was soaked in water for 24 hours. The sampleswere dried off, scribed and tested. Adhesion was analyzed for drysamples and after a 24 hour soak (Type I and Type III). As can be seenin FIG. 3, the coating according to the present disclosure had excellentadhesion for both wet and dry tests. All coatings with an adhesion of 8or higher were considered to be passing according to the criteria ofthis exemplary test.

FIG. 4 shows the test results for yet another test of samples preparedaccording to the present disclosure. In this test, coated 0.125 inchthick transparent composite samples were tested for wear in accordancewith the procedure described in ASTM D-1044-90, “Standard Test Methodfor Resistance of Transparent Plastics to Surface Abrasion”, also knownas a Taber Wear Test. The test included tow CS-10 wheels to which apredetermined weight of 500 gm load was applied. The wheels abraded thecoated substrate surface as the substrate was rotated on a table.Increase in haze is used as the criteria for measuring the severity ofabrasion. In this test, the samples were exposed until the hazeincreased by 5% as a result of abrasion. As can be seen in FIG. 4, thebare substrates exhibited very poor wear resistance, while substratescoated in accordance with the present disclosure showed improvedresistance to abrasion as compared to uncoated substrates, polysiloxanecoated substrates, and UV blocking layer and polysiloxane coatedsubstrates.

This disclosure describes an extremely durable transparent coating thatprovides UV protection to an underlying substrate. In one embodiment,the coating may be constantly monitored. Though this invention is aimedat transparent substrates, such as windows, any critical applicationwhere a hard, transparent protective coating that provides UV protectionis desired or required to protect a substrate is feasible.

While the disclosure has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims. It is therefore intended that the following appendedclaims and claims hereafter introduced are interpreted to include allsuch modifications, permutations, additions, and sub-combinations as arewithin their true spirit and scope.

1. A coating, comprising: a UV blocking layer; and a hard coating layerdisposed above the UV blocking layer; wherein the hard coating layer hasthe general formula SiO_(x)C_(y).
 2. The coating of claim 1, wherein theUV blocking layer is a polysiloxane coating that blocks greater thanabout 97% of UV radiation up to 375 nm.
 3. The coating of claim 1,wherein the UV blocking layer comprises a metal oxide.
 4. The coating ofclaim 1, wherein the hard coating comprises about 30% to about 35% Si,about 25% to about 30% C, and about 40% to about 45% O.
 5. The coatingof claim 1, further comprising multiple alternating layers of a softcoating and a hard coating.
 6. The coating of claim 1, wherein the UVblocking layer absorbs more than 97% of a UV light exposed to thecoating.
 7. The coating of claim 1, further comprising a hydrophobicouter layer deposited upon the hard coating layer.
 8. The coating ofclaim 1, wherein the UV blocking layer comprises a first layer and asecond layer, wherein the first layer provides UV blocking and thesecond layer provides a soft coating layer between the first layer andthe hard coating layer;
 9. The coating of claim 8, wherein the firstlayer has the general formula SiO_(x)C_(y).
 10. The coating of claim 8,wherein the soft coating comprises about 30% to about 35% Si, about 30%to about 35% C, and about 30% to about 35% O.
 11. The coating of claim8, wherein the UV blocking layer is a metal oxide layer.
 12. An articlecomprising: a substrate; and a coating deposited upon the substrate,wherein the coating comprises: a UV blocking layer disposed upon thesubstrate; and a hard coating layer; and wherein the hard coating layerhas the general formula SiO_(x)C_(y).
 13. The article of claim 12,wherein the article is a transparent composite
 14. The article of claim12, wherein the UV blocking layer comprises a metal oxide.
 15. Thearticle of claim 12, wherein the UV blocking comprises a first layer anda second layer, wherein the first layer provides UV blocking and thesecond layer provides a soft coating layer between the first layer andthe hard coating layer;
 16. The article of claim 15, wherein the firstlayer has the general formula SiO_(x)C_(y).
 17. The article of claim 15,wherein the coating comprises multiple alternating layers of the softcoating layer and the hard coating layer.
 18. A method of forming acoating on a substrate, comprising: providing a substrate; depositing UVblocking layer upon the substrate; and depositing a hard coating layerupon the UV blocking layer; wherein the hard coating has the generalformula SiO_(x)C_(y).
 19. The method of claim 18, wherein the UVblocking layer is deposited by depositing a coating layer comprising ametal oxide.
 20. The method of claim 18, wherein the UV blocking layeris deposited as a first layer providing UV blocking and a second layer,wherein the second layer is a soft coating layer.
 21. The method ofclaim 20, wherein the soft coating layer and the hard coating layer aredeposited by a plasma deposition process.
 22. The method of claim 21,wherein the plasma deposition process is continuous.
 23. The method ofclaim 21, wherein the plasma deposition process is discontinuous. 24.The method of claim 21, wherein more than one alternating layers of asoft coating layer and a hard coating layer are deposited.